Environmental life cycle assessment of wheat production using chemical fertilizer, manure compost, and biochar-amended manure compost strategies

Journal Pre-proof Environmental life cycle assessment of wheat production using chemical fertilizer, manure compost, and biochar-amended manure compost strategies

Zhixiang Jiang, Hao Zheng, Baoshan Xing PII:

S0048-9697(20)36873-X

DOI:

https://doi.org/10.1016/j.scitotenv.2020.143342

Reference:

STOTEN 143342

To appear in:

Science of the Total Environment

Received date:

6 August 2020

Revised date:

19 October 2020

Accepted date:

22 October 2020

Please cite this article as: Z. Jiang, H. Zheng and B. Xing, Environmental life cycle assessment of wheat production using chemical fertilizer, manure compost, and biocharamended manure compost strategies, Science of the Total Environment (2020), https://doi.org/10.1016/j.scitotenv.2020.143342

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© 2020 Published by Elsevier.

Journal Pre-proof Environmental life cycle assessment of wheat production using chemical fertilizer, manure compost, and biochar-amended manure compost strategies Zhixiang Jiang a, d, Hao Zheng b, c, Baoshan Xing d,*

a

College of Environmental Science and Engineering, Qingdao University, Qingdao

266071, China b

Institute of Coastal Environmental Pollution Control, Key Laboratory of Marine

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Environment and Ecology, Ministry of Education, Ocean University of China,

Laboratory for Marine Ecology and Environmental Science, Qingdao National

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c

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Qingdao 266100 China

Stockbridge School of Agriculture, University of Massachusetts, Amherst, MA 01003,

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USA

*Corresponding author:

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d

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Laboratory for Marine Science and Technology, Qingdao 266237, China

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* E-mail: [email protected] (Dr. Baoshan Xing), Tel.: 413-545-5212 (phone)

Journal Pre-proof Abstract Using manure compost (MC) as a substitute for chemical fertilizer (CF) has been regarded as an effective strategy to promote sustainable crop production. The application of biochar in compost production could significantly mitigate the emission of gaseous pollutants and improve compost quality. However, comprehensive investigations of the environmental performance of crop production using CF, MC, and biochar-amended MC strategies are scarce. Therefore, in this study, wheat

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production using four fertilizer strategies, including CF, MC, and biochar-amended

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MC with biochar addition rates of 5% (MCB5) and 10% (MCB10), was

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comparatively assessed in terms of their environmental performance using the life

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cycle assessment (LCA) method. Compared to the CF strategy, the majority of midpoint impact categories and all assessed damage categories (except for human

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health and resources in MCB10) were mitigated using the compost strategies.

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Furthermore, as the biochar application rate increased, the biochar-amended MC strategies remarkably decreased the impacts on the global warming potential,

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stratospheric ozone depletion, and land use, and greatly increased the impacts on ozone formation (human health), fine particulate matter formation, and terrestrial acidification. Overall, biochar-amended MC with a biochar addition rate of 5% (MCB5) is recommended as the optimal strategy due to its relatively low environmental impact. Moreover, combined with the results of the sensitivity analysis, biogenic air pollutant emissions derived from the compost and biochar production stages were identified as the most important hotspots contributing to the undesirable environmental impacts. These findings advance our understanding of the environmental performance of wheat production using biochar-amended MC. Keywords: biochar; carbon sequestration; compost; global warming; life cycle

Journal Pre-proof assessment; sustainable agricultural production

1 Introduction Food security is a great challenge worldwide due to decreased arable land resources, an increased global population, and aggravated climate change (Godfray et al., 2010; Wheeler and von Braun, 2013). As estimated by FAO et al. (2019), 820

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million people globally suffered from hunger in 2019, resulting in high demand for

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grain production. Thus, using limited arable land resources to produce more food is

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extremely important. It is widely recognized that chemical fertilizers (CFs) have made

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a significant contribution to the continuous increase in agricultural food production in the past decades. For example, the total annual quantity of CF applied increased from

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1.82 × 108 t in 2002 to 2.45 × 108 t in 2017, and correspondingly the total annual

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amount of grain yield increased from 76.7 × 108 t to 11.0 × 109 t during the same period (FAOSTAT, 2020). However, the increased CF application intensity, especially

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when overused, also brings a series of environmental burdens mainly caused by its low use efficiency, such as water eutrophication and high non-renewable resource input (Huang et al., 2017; Zhu et al., 2018a). Therefore, reducing the CF input to promote sustainable agricultural food production is urgently needed. The Ministry of Agriculture and Rural Affairs of China (2015) launched an action in 2015 with a goal of zero growth of CF input by the end of 2020. One important pathway recommended to achieve this aim is to increase the livestock manure fertilizer utilization to substitute for CFs. In developing countries, livestock manure is generally treated incorrectly, and only a fraction of the livestock manure is recovered as fertilizer, including fresh solid or liquid slurry manure, digested liquid slurry manure after

Journal Pre-proof anaerobic digestion, and composting (Xu et al., 2017). For example, currently, the rate of livestock manure recovered as fertilizer and used in the agricultural sector is estimated to be less than 50% in China (Ministry of Agriculture and Rural Affairs, 2017). Among the current applications, composting has been widely accepted as a promising alternative to untreated manure to produce high-quality organic fertilizer because it can stabilize organic matter and kill pathogens in raw manure due to the high temperatures accompanying the process (50‒60 oC) (Huang et al., 2006; Zhang

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et al., 2016). Furthermore, significantly lower soil emissions of N2O and CH4 were

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found for the application of manure compost (MC) than for fresh manure, which are

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attributed to the lower content of degradable C contained in MC than fresh manure

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(Jeong et al., 2019; Luo et al., 2019). However, composting of manure and its soil application are still at a relatively low level compared to the direct application of fresh

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et al., 2018).

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manure because higher inputs of material, cost, and time are required (Corbala-Robles

Biochar, a C-rich material, has been proposed as a highly effective and

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renewable additive to enhance nutrient retention, reduce emissions of CH4 and N-gases (NH3 and N2O), and improve the quality of composting products because of its unique properties such as a large surface area, rich pore structure, and high sorption capacity (Agyarko-Mintah et al., 2017; Lopez-Cano et al., 2016; Yang et al., 2020). Moreover, compared to MC, the application of biochar-amended MC may effectively increase soil organic C (SOC) stocks owing to its higher stability (Wang et al., 2014) and enhance the reduction of N2O emissions (Liu et al., 2019; Luo et al., 2017; Yang et al., 2020). According to the life cycle assessment (LCA) approach, environmental improvement benefits have been frequently reported for crop cultivation systems with biochar application compared to those without biochar (Dai

Journal Pre-proof et al., 2020; Hammond et al., 2011; Muñoz et al., 2017; Peters et al., 2015; Roberts et al., 2010). However, these LCA studies mostly aimed to clarify the environmental improvement potential of biomass utilization introduced with biochar technology; the effect of MC amended with biochar in the composting stage on the environmental performance of a crop cultivation system is still unknown. Additionally, using LCA better environmental and economic performances were also found for crop production using MC compared to CF (Zhong et al., 2013) or MC compared to untreated manure

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(Corbala-Robles et al., 2018). However, these studies are limited to assessing the

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environmental performance of MC-based crop production systems regarding a single

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environmental indicator or a specific manure treatment. Moreover, other

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comprehensive assessments involving multiple environmental indicators for a non-manure composting and land application system (i.e., municipal organic waste

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and food waste) have also been reported (Mancini et al., 2019; Saer et al., 2013), but

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various sources of organic waste (e.g., manure vs. food waste) could result in different environmental impacts based on their distinct components and characteristics.

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Therefore, a comprehensive and quantitative comparison of environmental performances for crop production under CF, MC, and biochar-amended MC fertilizer strategies cannot be accurately evaluated based on the published LCA studies mentioned above. This limits our understanding of environmental improvement potential for switching crop production from the currently dominant CF strategy to MC or biochar-amended MC strategies. To fill these knowledge gaps, a comprehensive environmental LCA of a wheat production system using different CF and compost strategies was conducted. The aims of this study are to 1) quantitatively assess the environmental impact of wheat production using four different fertilizer strategies; 2) compare the changes in

Journal Pre-proof environmental performance between CF and compost strategies, and examine the effect of the biochar addition rate on the environmental performance of the compost strategies; and 3) identify the hotspot stages that most significantly contribute to the overall result for the assessed environmental indicators. This study reports for the first time the comprehensive life cycle environmental performance of wheat production using CF, MC, or biochar-amended MC strategies. 2 Life cycle assessment (LCA) methodology

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2.1 Definitions of goal, system boundary, and functional unit of LCA

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The life cycle system boundary of wheat production using four fertilizer

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strategies, including conventional CF, MC, and two biochar-amended MC strategies,

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is illustrated in Fig. 1. The two biochar-amended MC strategies have biochar addition rates of 5% (MCB5) and 10% (MCB10) (Table 1), which represent the low and high

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levels of the biochar addition rates reported in previous studies, respectively (Table

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S1). For the compost strategies, MC, MCB5, and MCB10 were respectively employed to substitute half amount of CF used in the CF strategy. As shown in Fig. 1, the

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upstream stages of compost supply, including raw material (i.e., pig manure and wheat straw) collection and production of biochar (only for MCB5 and MCB10) and compost, field production, and transportation linking stages, are encompassed in the system boundary of the compost strategies. Notably, only one life cycle stage of wheat production in the field was included in the CF strategy (Fig. 1). Specifically, the manufacture of machinery, for example, those related to wheat straw field collection and transportation, involved in all life cycle stages was not included in the system boundary because of its negligible effect on the overall life cycle results (Hammond et al., 2011; Roberts et al., 2010). The organic raw materials (wheat straw and pig manure) were viewed as inevitable byproducts, along with wheat production and pig

Journal Pre-proof breeding, respectively. Thus the production processes of these two materials were also excluded from LCA calculation. In the present study, pig manure was selected as the representative manure to produce compost because of its large annual production quantity (i.e., the global quantity of pig feed in 2011 reached up to 9.01 × 108 capita) and wide distribution globally (Shober and Maguire, 2018). Wheat, the most cultivated crop in terms of area harvested (2.14 × 108 ha in 2018) worldwide (FAOSTAT, 2020), was selected as the

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representative crop. Considering a sustainable agriculture with waste recycling, the

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wheat straw was assumed to be used as biochar feedstock (Fig. 1). The goal of this

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study was to comparatively assess the environmental impact of wheat production

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2.2 Life cycle inventory analysis

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using different fertilizer strategies, and 1 t wheat grain yield was used as the

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The direct inputs of material and energy, and pollutant emissions at each life cycle stage were compiled from published studies. The indirect inputs of material and

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energy and pollutant emissions embedded in the production and supply of the consumed materials and energies (i.e., CF, diesel, and electricity) were taken from the database of the SimaPro software (PRé Consultants, 2017). Both the direct emission of diesel burned in haulage trucks and other operating machinery and the indirect material/energy input and pollutant emissions for diesel production were also taken from the SimaPro software database (PRé Consultants, 2017). The inventory analysis of whole life cycle stages, including field collection of wheat straw, wheat straw-biochar production, production of MC with or without biochar addition, wheat grain field production, and transportation linking stages, is comprehensively presented

Journal Pre-proof in “Supplementary Information”. Meanwhile, the key information specifically regarding the compost field application is also introduced below. 2.2.1 Substitution of CF by compost and application rates of fertilizers A lower global warming potential (GWP) has been reported frequently when partial CF was substituted by MC (or fresh manure) compared with CF application only, and attributed to the decreased use of CF and increased SOC content (Li et al., 2020; Montemayor et al., 2019; Yang et al., 2015). Furthermore, a higher

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eco-efficiency (economic and environmental trade-offs) was also identified when CF

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was partially substituted by fresh manure and ascribed to its higher economic profits

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and lower environmental impacts (Li et al., 2020). Moreover, a negative effect on the

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crop yield was found when more CF (e.g., full substitution) was substituted by MC (or fresh manure) (Zhang et al., 2020). Therefore, a substitution rate of 50% is

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recommended frequently based on its better environmental performance (Li et al.,

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2020; Yang et al., 2015) and highest crop yield increase rate (Du et al., 2020), and was also used in the present assessment. To calculate the application rates of MC, MCB5,

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and MCB10, an equivalent N input was used (Yang et al., 2015), meaning that the total amounts of N input (both from chemical and compost N) in each strategy were equivalent (Table 2).

2.2.2 Response of wheat grain yield to compost application Positive responses of crop yield to the application of MC or fresh manure in previous studies ranged from 6% to 20.9% (Agegnehu et al., 2016; Agegnehu et al., 2015; Du et al., 2020; Jiang et al., 2018; Yang et al., 2015). Unfortunately, these responses were not differentiated into MC and other manure-derived organic fertilizers (e.g., fresh manure and digested slurry) (Du et al., 2020; Jiang et al., 2018). Therefore, the specific response of the crop yield to the application of MC or

Journal Pre-proof biochar-amended MC cannot be directly acquired. Thus, based on an overview of the crop yield responses specifically to the application of MC and biochar-amended MC, the mean increase rates of wheat grain yield were assumed to be 18.7% for the MC strategy and 17.7% for the MCB5 and MCB10 strategies, respectively, compared to the CF strategy. 2.2.3 Responses of SOC stock and non-CO2 greenhouse gas (GHG) emissions to compost application

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The change in SOC stock after MC application is one of the most important

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factors that could greatly affect the overall LCA result of the GWP. An enhanced SOC

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stock after compost application has been reported in previous studies (Ding et al.,

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2012; Li and Han, 2016; Tian et al., 2009; Xin et al., 2016). However, whether the increased SOC content was derived from the added compost or reduced native SOC

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decomposition was not well differentiated. Commonly, an integrated indicator of the

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increase in the initial SOC content (in %) was reported in previous studies (Table S2). Additionally, it has been widely accepted that the stable C contained in biochar could

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be sequestrated in soil long-term (e.g., > 100 years) (Peters et al., 2015; Roberts et al., 2010). Therefore, the change in SOC stock after compost application in this assessment includes two aspects: i) a % increase in initial SOC content for all compost strategies, and ii) an additionally increased SOC stock derived from the C sequestrated in biochar for the MCB5 and MCB10 strategies only. In the wheat production stage, the soil emissions of non-CO2 GHG (e.g., CH4 and N2O) derived from fertilizer utilization were also considered for all the strategies. More detailed information regarding the compost field application can be found in the “S1.4 Wheat field production” section of the “Supplementary Information”. The comprehensive life cycle inventory data for each fertilizer strategy for wheat

Journal Pre-proof production are listed in Tables S3‒S6. 2.3 Life cycle impact assessment The SimaPro software (version 8.5.0; PRé Consultants, 2017) was employed to estimate the life cycle environmental impacts of wheat production with different fertilizer strategies using the ReCiPe 2016 method, which determines indicators at the midpoint and endpoint level. The default hierarchist version was used in this study. Eighteen impact categories (Table 1) and three damage categories, including human

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health (unit: DALY), ecosystems (unit: species.yr-1), and resources (unit: USD2013),

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were analyzed at the mid and endpoints, respectively, to compare the environmental

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performance of wheat production using different fertilizer/compost strategies.

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2.4 Sensitivity analysis

Sensitivity analyses were conducted to explore the sensitivity of the LCA results

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to the changes in key parameters assumed in the LCA model. Six parameters,

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including the field burning rate of wheat straw, wheat grain yield, rate of substitution of the composting product for chemical N fertilizer, CH4 emission factor of

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composting, SOC content, and heat recovery rate of biochar production, were analyzed because of their higher uncertainty regarding the research assumptions (Huang et al., 2013). The LCA results of both the midpoint and endpoint categories under ±50% of the tested parameters were assessed, and the sensitivity coefficient (SE) was calculated using the following equation (Jiang et al., 2020a): 𝑆𝐸𝑖𝑗 = (

𝑉𝑖𝑗(50%) − 𝑉𝑖𝑗(−50%) )/50% 2𝑉𝑖(𝑜𝑟𝑖𝑔𝑖𝑛𝑎𝑙)

where 𝑉𝑖(50%) and 𝑉𝑖(−50%) are the assessed values of the ith impact and damage category under -50% and 50% of the j-th tested parameter, respectively, and 𝑉𝑖(𝑜𝑟𝑖𝑔𝑖𝑛𝑎𝑙) is the originally assessed value of the i-th impact/damage category.

Journal Pre-proof 2.5 Data analysis The LCA results were the output by the SimaPro software (version 8.5.0; PRé Consultants, 2017), and the data processing was conducted in Microsoft Excel 2016. The output of the figures was analyzed using Microsoft Excel 2016 and Origin 2017. 3 Results and discussion 3.1 Impact categories: midpoint results 3.1.1 Global warming potential (GWP)

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The quantitative results of the life cycle environmental impacts of the midpoint

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categories are listed in Table 3, and more detailed information regarding the GWP

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results for each life cycle stage of the four strategies can be found in Tables S8‒S11.

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The highest life cycle GWP was observed for the MC strategy and estimated to be 1.33×103 kg CO2-eq (t wheat grain)‒1. A similar result [1.33×103 kg CO2-eq (t wheat

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grain)‒1] was reported by Yang et al. (2015), who conducted a three-year field

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experimental study of wheat production with half of the chemical N fertilizer substituted by pig manure compost. However, they did not consider the changes of

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SOC content and GHG emissions during the upstream stages of pig manure compost supply. Additionally, the estimated life cycle GWP in the present study was 1.33×103 kg CO2-eq (t wheat grain)‒1, equivalent to 1563 kg CO2-eq (t MC)‒1, which is approximately six times higher than that reported by Zhong et al. (2013) [240 kg CO2-eq (t MC)‒1]. This large variation could be explained by the different emission factors of biogenic CH4 and N2O assumed in the stages of composting and MC soil application. Furthermore, lower values of GWP than those assessed in the present study were observed when CF was partially substituted by other manure-derived fertilizers in a maize-wheat rotation system. For example, the estimated GWP values ranged between 188‒567 kg CO2e (t grain)‒1 when about half the amount of CF was

Journal Pre-proof substituted by fresh solid or liquid slurry manure (Li et al., 2020; Huang et al., 2018). However, GHG emissions from manure fertilizer production were not considered in those studies. Moreover, extremely low GWP values [ranging from 45‒100 kg CO2e (t grain)‒1] were also found for a case of digested manure slurry application, to which the GHG offset due to bioenergy production from digested manure slurry production was the major contribution (e.g., bioenergy from CH4) (Montemayor et al., 2019). In contrast, a much higher GWP of 3270 kg CO2-eq (t rice grain)‒1 for a green manure

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fertilizer rice production system, compared to that for the MC strategy in this study,

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was observed by Bacenetti et al. (2016). This may be explained by the high

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application rate of compost (22.5 t ha‒1 vs. 7.62 t ha‒1) and a different crop cultivation

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system (paddy rice vs. wheat) in the study by Bacenetti et al. (2016). For example, Zhang et al. (2020) found that the CH4 emission intensity was significantly increased

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(48‒82%) in the paddy rice cultivation system, while there was no significant change

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in the upland cultivation system with CF substituted by manure-derived fertilizer. Compared to the CF strategy, the GWP value increased by 9.33% in the MC

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strategy, while it greatly decreased by 36.9% and 48.2% in the MCB5 and MCB10 strategies, respectively (Table 3). Regarding CF soil application and irrigation, the CF products and energy input were identified as the two main hotspots for the GWP, which contributed 51.4% and 29.5% of the life-cycle GHG emissions, respectively (Fig. 2a). Considerable amounts of non-renewable material/energy consumption, mainly through chemical N and diesel production and supply, were the main contributors to the GHG emissions (Montemayor et al., 2019; Zhu et al., 2018b). Therefore, decreasing the chemical N input and substituting CF by MC or biochar-amended MC could mitigate the GWP from chemical production (Huang et al., 2018; Li et al., 2020). At the same time, the potential for GWP mitigation of this

Journal Pre-proof stage could be further enhanced by the elevation of the SOC content due to MC or biochar-amended MC application. Overall, the GWP from the field production stage was greatly mitigated from 1.21×103 kg CO2-eq (kg wheat grain)‒1 in the CF strategy to 254‒553 kg CO2-eq (kg wheat grain)‒1 in the MC, MCB5, and MCB10 strategies (Tables S8‒S11). These results are supported by findings reported in previous studies (Huang et al., 2018; Li et al., 2020), where the GWP was mitigated by 17.8‒48.0% when CF (40‒50%) was partially replaced by fresh solid or liquid manure in the

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maize-wheat rotation system. However, the GWP mitigation benefit derived from

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MC/biochar-amended MC substitution was partially or totally offset by the increased

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GWP originating from the additional upstream stages of compost supply. As

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illustrated in Fig. 2b‒d, the compost production stage was found to be a critical hotspot for the life cycle GWP, which contributed 41.6%, 22.3%, and 21.6% to the

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life-cycle GHG emissions in the MC, MCB5, and MCB10 strategies, respectively.

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Likewise, Bacenetti et al. (2016) found that the life cycle GWP of an organic rice production system was dominated by the compost production stage, accounting for

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49.0% of the life cycle GWP. Similar results were also reported in other studies (Saer et al., 2013; Zhong et al., 2013). In conclusion, more attention should be paid to the reduction of GHG emissions embedded in the upstream stages of compost supply. The comparative results between the MC, MCB5, and MCB10 strategies indicate that the life cycle GWP of wheat production could effectively be reduced using MCB5 and MCB10, and that the higher rate of biochar addition induced a larger mitigation of life cycle GWP. These benefits can be explained by two aspects. On the one hand, the amount of biogenic GHG emissions from the compost production stage was greatly reduced when biochar was introduced (Chen et al., 2020). The GHG source stucture analysis (Fig. 3a) reveals that the biogenic GHG (CH4 and N2O) from the compost

Journal Pre-proof production stage accounted for 50.4% [680 kg (t wheat grain)‒1] of the life cycle GWP in the MC strategy, while it decreased to 26.1% [256 kg (t wheat grain)‒1] and 24.2% [257 kg (t wheat grain)‒1] in the MCB5 and MCB10 strategies, respectively. On the other hand, the additional increase in SOC content derived from biochar-C also contributed to a considerable decrease in the overall GWP. For example, the total amounts of increased SOC for the MCB5 and MCB10 strategies were 535 and 686 kg CO2e (t wheat grain)‒1, respectively, which were much higher than those for the MC

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strategy [401 kg CO2e (t wheat grain)‒1] (Tables S8–S11).

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As shown in Fig. 3b, the portion of GHG emissions from the additional

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fossil-energy accounted for 31.5‒37.4% of the total fossil-GHG emissions. This result

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demonstrates that the additional fossil fuel consumed in the upstream stages of compost supply was an important contributor to the life cycle GWP in the MC, MCB5,

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and MCB10 strategies. Additionally, the avoided wheat straw burning due to wheat

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straw collection and avoided fossil-fueled heat generation substituted by biogenic heat

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produced from biochar production contributed to the lower life cycle GWP (Fig. 2b‒

3.1.2 Impact categories affected by CF and fossil fuel utilization In the CF strategy, the impact categories of IR and M-EU were mainly dominated by the CF input, which accounted for 53.8% and 79.5% of life cycle IR and M-EU, respectively (Fig. 2a). Thus, the values of these two impact categories markedly decreased in the three compost strategies due to the substitution of CF by MC or biochar-amended MC (Table 3). The CF products and energy input were identified as the main contributors to the impact categories F-EU, T-ET, F-ET, M-ET, HCT, HNCT, MRS, and FRS in the CF strategy (Fig. 2a), indicating that their values could be decreased by MC/biochar-amended MC substitution, but increased by the

Journal Pre-proof additional energy consumption during wheat straw collection, and compost production and field application (Tables S9‒S11). Overall, the impacts of F-EU, F-ET, M-ET, and HNCT were enhanced in the three compost strategies compared to the CF category (Table 3), indicating that they were substantially affected by the increased diesel consumption relative to the MC/biochar-amended MC substitution. In contrast, the impacts of T-ET, HCT, and FRS were mitigated (Table 3), suggesting that the MC/biochar-amended MC substitution had a greater effect on the results of T-ET,

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HCT, and FRS than the increased diesel consumption. Similar reductions of T-ET,

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HCT, and FRS were also reported in previous studies (Li et al., 2020; Montemayor et

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al., 2019), where the impacts of T-ET, HCT, and FRS were consistently reduced by

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4.38‒4.88%, 40.3‒44.1%, and 28.9‒96.0%, respectively, when a certain quantity of

rotation system.

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CF (50‒80%) was replaced by fresh or digested manure fertilizers in a maize-wheat

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3.1.3 Impact categories affected by biogenic air pollutant emission The values of the impact categories OF-HH, FPMF, and OF-TE were much

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lower in the MC than in the CF strategy (Table 3). This could be mainly attributed to the fact that no wheat straw fields were burned, resulting in zero emissions of air pollutants, including particulates (< 2.5 μm), SO2, NOx, and non-methane volatile organic compounds. For example, the values of life cycle OF-HH, FPMF, and OF-TE could be mitigated by -28.2%, -59.2%, and -32.6%, respectively, in the MC strategy (Fig. 2b). However, they were higher in the MCB5 and MCB10 strategies compared to MC, with the values of life-cycle FPMF in MCB5 and MCB10 even being higher than those in the CF strategy (Table 3). This result could be explained by the increased emissions of SO2 and NOx in the biochar production stage, which were 20.9‒47.9% and 35.2‒65.8% of the life-cycle OF-HH, FPMF, and OF-TE in MCB5 and MCB10,

Journal Pre-proof respectively (Fig. 2c and d). An adverse effect on the environment due to pollutant emissions (i.e., particles) during biochar production was also observed in a previous study (Sparrevik et al., 2013). It is important to note that TA substantially increased in all compost strategies compared to CF, and the highest value was observed in MCB10 (Table 3). The compost production stage in the MC strategy and the production stages of biochar and compost in the MCB5 and MCB10 strategies, respectively, were found to be the

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hotspots of life cycle TA (Fig. 2b‒d). This result is consistent with the increased

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emissions of NH3 from the composting stage, and SO2 and NOx from the biochar

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production stage, which were the main air pollutants related to TA (He et al., 2018) in

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the compost strategies. The significant contribution of the NH3 emissions of the composting stage to the total TA result was also observed in other pig manure

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treatment systems (Ramirez-Islas et al., 2020). In another previous study,

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Chatzisymeon et al. (2016) reported that organic pepper cultivation had a significantly lower impact on TA than conventional cultivation. However, manure was used directly,

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and no impact on TA from compost production was considered in their study. Regarding SOD, a much higher value was observed in the MC than in the CF strategy (Table 3). As illustrated, in the CF strategy the SOD was dominated by the CF input (56.5%) and soil emission of N2O (41.3%) (Fig. 2a). In the MC strategy, the compost production stage contributed 45.6% of the life cycle SOD (Fig. 2b), indicating that this stage contributed to a greater impact on SOD than to mitigating SOD derived from MC/biochar-amended MC substitution. Furthermore, the values of life cycle SOD were lower in the MCB5 and MCB10 strategies than in the CF strategy (Table 3) because biochar reduced the biogenic N2O from the composting stage. 3.1.4 Other impact categories

Journal Pre-proof Much lower values of life cycle LU were observed in all the compost strategies compared to CF (Table 3). Notably, MCB5 and MCB10 had higher reduction potentials than MC, which was mainly attributed to the avoided fossil-fueled heat generation (Fig. 2c and d). This result indicates that the biochar-amended MC strategies should be superior to the one without biochar when faced with a situation of limited land resources. Trends of WC were found to be similar for the CF and compost strategies (Table 3), with direct freshwater consumption primarily

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contributing to the impact on WC in all the strategies (Fig. 2). The decreased values of

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WC for the compost strategies indicates a positive increase in the freshwater use

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efficiency of wheat production under the compost strategies, which probably resulted

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from the dilution effect of the increased wheat grain yield. Furthermore, the small changes in WC in other life cycle stages of wheat production in all the compost

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strategies (Fig. 2b‒d) also imply that the MC/biochar-amended MC substitution or

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biochar application had very little effect on the life cycle result of WC. 3.2 Damage categories: endpoint results

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The quantitative results of the life cycle environmental impacts at the endpoint level, including human health, ecosystems, and resources, are illustrated in Table 4. For all three damage categories the values were lower in the compost strategies (except for human health and resources in MCB10) than in the CF strategy, and the decrease in damage to human health, ecosystems, and resources was 11.5‒13.6%, 6.27‒16.9%, and 3.35‒8.04%, respectively (Table 4). These results indicate that lower environmental damage could be obtained by shifting wheat production from the CF to compost strategies. A consistent mitigation of the damage to human health (decreased by 22.2‒39.9%) was also reported by Li et al. (2020), where 50% of CF was substituted by fresh solid or liquid manure. Freshwater input was identified as the

Journal Pre-proof critical contribution to the damage to human health and ecosystems in all the fertilizer strategies (Fig. 4). Apart from the freshwater input, these two damage categories were also dominated by the compost production in the MC strategy (Fig. 4b). However, in MCB5 and MCB10, the additional stage of biochar production exerted a larger effect on the damage to human health and ecosystems than the compost production stage (Fig. 4c and d). The environmental damage performance of wheat production using the compost strategy could be effectively mitigated by introducing biochar into the

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composting stage; however, it would again increase when a high biochar application

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rate was used. Therefore, the MCB5 strategy with 5% biochar addition during the

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composting stage is recommended. Notably, the damages to human health and

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ecosystems were also potentially decreased by the avoided pollutant emissions due to zero wheat straw burning (Fig. 4b‒d), confirming the positive environmental impact

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of recycling crop straw (Jiang et al., 2020a). Regarding resources damage, its life

na

cycle result was mainly dominated by CF (52.1%) and energy (45.1%) in the CF strategy (Fig. 4a). Thus, the damage to resources could be decreased by the

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MC/biochar-amended MC substitution, but increased due to the additional diesel input from the upstream stages of compost supply and field application of compost in the compost strategies (Fig. 4b‒d).

Very few published studies have been carried out that compare the environmental performance of wheat production using CF and different MC/biochar-amended MC strategies. For example, Ramirez-Islas et al. (2020) compared the environmental performance of pig manure treatments with different energy production scenarios, but the compost field application was only viewed as one life cycle stage of byproduct use. In two other studies, by Luo et al. (2014) and Pergola et al. (2018), the environmental, economic, and energetic performances of on-farm manure management involving

Journal Pre-proof different compost production crafts were assessed without considering the compost field application. Furthermore, other impact and damage indicators in addition to the GWP, as discussed in the present study, have been reported with large variation in previous studies. This is due to the different life cycle impact assessment methods employed, for example, the ReCiPe 2016 method here vs. the Center of Environmental Science (CML-IA, 2013) (Ramirez-Islas et al., 2020) and International Reference Life Cycle Data System (ILCD) (Bacenetti et al., 2016; Ten Hoeve et al.,

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2019) methods in previous studies. Therefore, based on the different study objectives

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and life cycle impact assessment methods mentioned above, it is currently difficult to

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comprehensively compare our results with those of previous studies (He et al., 2018).

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3.3 Sensitivity analysis

Sensitivity analyses for the impact and damage categories were conducted to

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explore the LCA results affected by the six tested key parameters (Figs. 5 and 6). A

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higher sensitivity coefficient (SE) indicates a higher sensitivity of the LCA result to the corresponding parameter, and a negative (positive) SE implies that the value of the

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LCA result will decrease (increase) when the corresponding parameter increases. Changes in the field burning rate of wheat straw exerted a significant effect on the impact categories OF-HH, FPMF, and OF-TE (SE from -1.22 to -0.39) (Fig. 5a), and the damage category human health (SE from -0.36 to -0.23) (Fig. 6a) in all the compost strategies. The negative SE also implies that the environmental performance of wheat production with a higher field burning rate of wheat straw could be improved using compost strategies. This is consistent with the findings that the reductions in OF-HH, FPMF, and OF-TE in the compost strategies were dominated by the zero wheat straw field burning (Fig. 2). In all compost strategies, all impact and damage categories were consistently affected by the increase rate of wheat grain yield,

Journal Pre-proof and the SE values were around -0.15 (Fig. 5b and Fig. 6b). This was probably because the organic fertilizer (e.g., MC or biochar-amended MC) input per ton wheat grain yield could be reduced when the total wheat grain yield further increased, implying that the negative environmental impacts derived from the MC or biochar-amended MC production and supply were correspondingly offset. As illustrated in Fig. 5c, changes in the substitution rate of chemical N significantly affected all the impact categories except for IR, FRS, and WC, and the

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effects of the MCB5 and MCB10 strategies were generally higher than those of the

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MC strategy. Furthermore, contrary directions were observed among differently

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oriented types of impact categories. For example, CF-oriented categories, including

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F-EU, M-EU, T-ET, F-ET, and M-ET, showed more negative SEs than other categories, implying that these environmental impacts could be further mitigated with

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higher substitution for chemical N. The value of the biogenic air pollutant-oriented

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category of TA, for which the SE ranges from 0.75 to 0.85 (Fig. 5c), could be greatly enhanced when the chemical N fertilizer was replaced with higher amounts of MC or

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biochar-amended MC. Regarding the damage categories, the environmental damages of all categories in the compost strategies could further increase with an increasing rate of chemical N substitution, which was supported by positive SE values (Fig. 6c). This suggests that a higher environmental impact, even when negative compared to the CF strategy, could be generated under a relatively high rate of chemical N substitution by MC or biochar-amended MC. However, recent studies have reported that organic agriculture, in which CFs were completely substituted by organic compost, exhibited a better environmental performance than conventional agricultures (He et al., 2018; He et al., 2016; Zhu et al., 2018b). For example, He et al. (2018) found that the aggregated LCA impact index, a normalizing indicator of the impact

Journal Pre-proof values, of organic agricultural systems (0.68‒0.80) was substantially lower than that for conventional agricultural system (9.65), suggesting a positive mitigation of the environmental impact by shifting the conventional agriculture to organic agriculture. However, this remarkable mitigation is inconsistent with the results presented in the present study because the environmental impacts embedded in composting stage were either not considered (Chatzisymeon et al., 2016; Zhu et al., 2018b) or underestimated (He et al., 2018). For example, the emission factors of CH4, N2O, and NH3 during the

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cattle manure composting stage in the study by He et al. (2018) were 0.65, 0.05, and

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0.96 kg (t compost)‒1, respectively, much lower than those used in the present study of

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12.7, 1.10, and 5.36 kg (t MC)‒1 for the three gases, respectively (Table S4).

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Underestimating the environmental impacts embedded in upstream of organic compost supply could lead to a misleading understanding of the development of

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organic agriculture. Notably, organic agriculture usually yields a lower agricultural

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product yield than the conventional agriculture, and thus the former generates a larger GWP and higher land occupation per unit agricultural product yield than the latter (He

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et al., 2018; He et al., 2016). With the world facing an increasing scarcity of arable land resources and the severity of global climate change, organic agriculture, as mentioned above, may not be suitable for large-scale development. However, combining

biochar-amended

MC

strategies

(e.g.,

MCB5)

with

organic

agriculture may mitigate these negative impacts. Therefore, increasing the agricultural product yield by optimizing the combination of MC and CF use could be a promising strategy, especially for biochar-amended MC production and application. Only the impact category of GWP was affected at a relatively high sensitivity level by changes in the parameters CH4 emission factor of composting and increase rate of SOC content in all the compost strategies (Fig. 5d and e), implying the

Journal Pre-proof importance of the contributions of these two parameters to the life cycle GWP result. The damage categories human health and ecosystems were less sensitive to the changes in these two parameters, especially for MCB5 and MCB10 (Fig. 6d and e). The positive SE (0.17 to 0.29) of the CH4 emission factor of composting (Fig. 5d) further supported the finding that the biogenic GHG (CH4 and N2O) generated from the composting stage was a critical factor in promoting the life cycle GWP of the compost strategy. Therefore, the life cycle GWP of the compost strategy would be

of

mitigated if the biogenic GHG emissions were controlled well in different ways, such

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as through biochar application in MCB5 and MCB10. Moreover, other regulatory

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measures, such as the forced aeration (Pardo et al., 2015) and a vent gas disposal

re

device (Bruun et al., 2014), could also effectively decrease biogenic GHG emissions from composting. However, the increased energy and material inputs and cost for the

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additional equipment for these measures could lead to additional GHG emissions,

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which may offset the GWP mitigation (Jiang et al., 2011; Zhong et al., 2013). Therefore, the life cycle GWP of wheat production using the compost strategy under

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different pig manure composting models should be investigated further. As expected, the life cycle GWP of the compost strategies could be negatively affected by an increase in SOC content, which was evidenced by the negative SE values ranging from -0.64 to -0.30 (Fig. 5e), indicating an important contribution to the mitigation of life cycle GWP derived from the increased SOC content due to MC or biochar-amended MC application. Improvements in soil aggregate stability and aggregate-associated SOC fractions have been suggested as the key contributions to the increased SOC content after organic compost application (Du et al., 2014; Mi et al., 2018; Xin et al., 2016; Zheng et al., 2018). For example, Yu et al. (2012) found that the SOC content increased by 72.0‒124% due to the increased mass proportion of

Journal Pre-proof macro-aggregates (> 250 μm) amended with agricultural residue compost. The increase rate of the SOC content was assumed to be consistent for both MC and biochar-amended MC in the present assessment, due to a lack of data regarding the effect of biochar-amended MC on the SOC content. However, the interactions of MC or biochar-amended MC with native soil organic matter may vary in a real soil environment, which may further generate different effects on SOC. It has been reported that the properties of biochar-amended MC (e.g., cation exchange capacity

of

and O-containing functional groups and minerals) could be greatly improved by

ro

biochar-mediated interactions between minerals/inorganic compounds and organic

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compounds (Archanjo et al., 2017; Jiang et al., 2020b; Khan et al., 2016; Zeng et al.,

re

2015). This may promote the interaction between biochar-amended MC and native soil organic matter to form stable soil aggregates and thus benefit soil C accumulation.

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Moreover, the stability of biochar-amended MC would be higher than that of MC

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when applied to soils, as evidenced by the higher humification extent of biochar-amended MC (Dias et al., 2010; Wang et al., 2014; Zhang et al., 2016).

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Consequently, the biochar-amended MC may result in a greater increase in the soil recalcitrant C pool compared to MC. In summary, MCB5 and MCB10 strategies may result in a larger mitigation potential of life cycle GWP than MC alone, which should be further verified in future studies. The life cycle LU showed a remarkable sensitivity to changes in the heat recovery rate of biochar production, with the SE ranging from -3.25 in the MCB10 strategy to -2.33 in MCB5 (Fig. 5f), suggesting that increasing the heat recovery rate of the biochar production could save more land resources. Other impact categories and all damage categories (Figs. 5f and 6f) were found to be less affected by changes in this parameter. These sensitivity analysis results further confirm that the recovery

Journal Pre-proof of heat from byproduct (bio-oil and pyrolytic gas) combustion during biochar production could contribute to greater advantages in the biochar-amended MC strategies than the MC strategy regarding land use saving. 4 Conclusions Our LCA results demonstrate that the environmental performance of wheat production could be greatly improved by shifting the conventional CF strategy to manure compost (particularly the biochar-amended manure compost) strategies.

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Furthermore, biogenic air pollutant emissions from composting and biochar

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production stages were identified as the most important hotspots contributing to

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undesirable environmental impacts, which should be the focus of future studies. Based

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on a comparison of the LCA results of the three compost strategies, MCB5 with a low biochar addition rate of 5% is recommended as a suitable strategy for wheat

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production because of its relatively low environmental impact. It was also noted that

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the biochar-amended manure compost strategy has a significant potential for GWP mitigation and used less land for wheat production. Hence, biochar-amended manure

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compost may be more relevant for in mitigating the growing threat of global warming and land resource shortage. Moreover, the biochar-amended compost strategy could also be suitable for the construction of ecological agriculture models with low environmental impacts by enhancing the efficiency of material and energy recycling within the agricultural sector. However, an economic analysis, another important evaluation criterion beyond the environmental performance, of wheat production under different fertilizer strategies is not addressed in the present study, and should be conducted in future work. Overall, this study provides useful information for developing a feasible practice for sustainable agriculture production using agricultural waste in the form manure and biochar from crop straw.

Journal Pre-proof

Acknowledgements This research was supported by the National Natural Science Foundation of China (41703084), Shandong Key Research and Development Program-Science and Technology

Innovation

Project

(2018CXGC0304),

USDA-NIFA

Hatch

program/UMass CAFE (MAS 00549), and UMass Amherst Conti Faculty fellowship. Z.X.J thanks Shandong Provincial Education Department for supporting him to study

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lP

re

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at UMass Amherst for a year.

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Journal Pre-proof Fig. 1. System boundaries of wheat production using the CF, MC, MCB5, and MCB10 strategies. For the CF strategy, only one life cycle stage of wheat production in the field was included. For the compost strategies, half of the CF used in the conventional CF strategy was substituted by MC, MCB5, or MCB10 based on the N equivalent. Fig. 2. Hotspots identification of impact categories for CF (a), MC (b), MCB5 (c), and MCB10 (d) strategies. WS-C: wheat straw collection. Comp.-P: compost production. Trans.: transportation of material and product (e.g., wheat straw, pig manure, biochar, and compost). I-CF, I-Pest., I-Energy, and I-Other: inputs of chemical fertilizer (N/P/K), pesticides, fossil energy, and others (fresh water and seed). Soil-Emis.: soil non-CO2 emission (e.g., N2O and CH4). Soil-C: soil organic C content. AWFB: avoided or zero wheat straw field burning. AHP: avoided heat production.

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Fig. 3. Greenhouse gas (GHG) emission structure categorized by fossil and biogenic derived sources (a), fossil-GHG emissions from the upstream stages of compost supply and the stage of compost field spreading, and the total amount of fossil-GHG emission (T-fossil fuel CO2-eq) (b). Bio-CH4 (Comp.) and bio-N2O (Comp.): biogenic CH4 and N2O (CO2-eq) emitted during the composting stage. bio-CH4 (soil) and bio-N2O (soil): biogenic CH4 and N2O (CO2-eq) emitted from soil during wheat production stage.

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Fig. 4. Hotspots identification of damage categories for CF (a), MC (b), MCB5 (c), and MCB10 (d) strategies. WS-C: wheat straw collection. Comp.-P: compost production. Trans.: transportation of material and product (e.g., wheat straw, pig manure, biochar, and compost). I-CF, I-Pest., I-Energy, and I-Other: inputs of chemical fertilizer (N/P/K), pesticides, fossil energy, and others (fresh water and seed). Soil-Emis.: soil non-CO2 emission (e.g., N2O and CH4). Soil-C: soil organic C content. AWFB: avoided wheat straw field burning. AHP: avoided heat production.

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Fig. 5. Sensitivity results of the impact categories. Field burning rate of wheat straw (a). Wheat grain yield (b). Substitution rate of chemical N fertilizer (c). CH4 emission factor of composting (d). Soil organic C content (e). Heat recovery rate during biochar production (f). A higher sensitivity coefficient (SE) indicates a higher sensitivity of the LCA result to the corresponding parameter, and a negative (positive) SE implies that the value of the LCA result will decrease (increase) when the corresponding parameter increases. Fig. 6. Sensitivity results of the damage categories. Field burning rate of wheat straw (a). Wheat grain yield (b). Substitution rate of chemical N fertilizer (c). CH4 emission factor of composting (d). Soil organic C content (e). Heat recovery rate during biochar production (f). A higher sensitivity coefficient (SE) indicates a higher sensitivity of the LCA result to the corresponding parameter, and a negative (positive) SE implies that the value of the LCA result will decrease (increase) when the corresponding parameter increases.

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Table 1. Abbreviation lists and units (when applicable) of the fertilizer products and impact category at midpoint level according to ReCiPe 2016 methodology Fertilizer product Abbreviation Fertilizer product Abbreviation Chemical fertilizer CF Manure compost MC Manure compost with MCB5 Manure compost with MCB10 biochar addition rate of biochar addition rate of 5% 10% Impact category Abbreviation Impact category Abbreviation Global warming potential GWP Terrestrial ecotoxicity (kg T-ET (kg CO2-eq) 1,4-DCB) Stratospheric ozone SOD Freshwater ecotoxicity (kg F-ET depletion (kg CFC11-eq) 1,4-DCB) Ionizing radiation (kBq IR Marine ecotoxicity (kg M-ET Co-60-eq) 1,4-DCB) Ozone formation (human OF-HH Human carcinogenic HCT health) (kg NOx-eq) toxicity (kg 1,4-DCB) Fine particulate matter FPMF Human non-carcinogenic HNCT formation (kg PM2.5-eq) toxicity (kg 1,4-DCB) Ozone formation OF-TE Land use (m2 a crop-eq) LU (terrestrial ecosystems) (kg NOx-eq) Terrestrial acidification TA Mineral resource scarcity MRS (kg SO2-eq) (kg Cu-eq) Freshwater F-EU Fossil resource scarcity (kg FRS eutrophication (kg P-eq) oil-eq) Marine eutrophication M-EU Fresh water consumption WC (kg N-eq) (m3)

Journal Pre-proof Table 2. Inputs of chemical N fertilizer and manure compost products under different wheat production strategiesα. Chemical N MC product MCB5 product MCB10 product ‒1 ‒1 ‒1 ‒ Strategy kg N ha t ha kg N t ha kg N ha t ha‒1 kg N ha‒ 1 1 ha‒1 β CF 316 0 0 0 0 0 0 MC 158 7.62γ 158 0 0 0 0 MCB5 158 0 0 8.32 158 0 0 MCB10 158 0 0 0 0 8.83 158 α

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The equivalent N input was used to calculate the application rates of fertilizer and compost under different strategies. β Data originated from Zhu et al. (2017). γ The application rates of different compost products were determined by the substituted amount of N (158 kg ha-1) and the N contents of compost products. The detailed calculation of N contents in the different compost products can be seen in the Table S7.

Journal Pre-proof Table 3. Life cycle results of impact category (midpoint) under the four wheat production strategies.

OF-TE/kg NOx-eq TA/kg SO2-eq F-EU/kg P-eq M-EU/kg N-eq T-ET/kg 1,4-DCB F-ET/kg 1,4-DCB M-ET/kg 1,4-DCB HCT/kg 1,4-DCB HNCT/kg 1,4-DCB LU/m2a crop-eq MRS/kg Cu-eq FRS/kg oil-eq WC/m3

3.00E +00 1.71E +00 3.05E +00 4.83E +00 2.51E -01 2.31E -01 2.88E +03

Quan tity

7.66E+ 02

-36.9

6.29 E+02

1.65E-0 2 1.65E+ 01

-10.4

1.63 E-02 1.57 E+01

-11.2

-35.1

2.35E+ 00

-21.4

2.75 E+00

-8.08

-34.2

1.76E+ 00

3.05 E+00

78.5

-38.7

2.22E+ 00

-27.2

2.54 E+00

-16.8

158

1.92 E+01

298

2.80E-0 1 4.94E-0 2 2.43E+ 03

11.2

2.86 E-01 4.81 E-02 2.35 E+03

13.9

8.38

2.78E+ 01

9.87

2.82 E+01

11.6

10.2

3.93E+ 01

11.6

3.99 E+01

13.3

-16.8

3.06E+ 01

-13.0

3.25 E+01

-7.55

23.1

1.66E+ 03

29.1

1.77 E+03

37.1

-53.4

2.91E+ 01

-85.4

-4.51 E+01

-123

-0.81

6.95E+ 00

6.37

7.56 E+00

15.8

-10.6

1.71E+ 02

-7.01

1.80 E+02

-1.99

-16.8

6.47E+

-16.1

6.47

-16.1

28.7 -64.6

140

9.39 -78.1

2.53E +01 3.52E +01 3.52E +01 1.29E +03 1.99E +02 6.53E +00 1.84E +02 7.71E

-66.2

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1.84E -02 4.88E +01

% change to the CF strategy -48.2

% change to the CF strategy

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FPMF/kg PM2.5-eq

1.33 E+0 3 2.36 E-02 1.73 E+0 1 1.95 E+0 0 1.12 E+0 0 1.87 E+0 0 1.16 E+0 1 2.75 E-01 5.04 E-02 2.50 E+0 3 2.74 E+0 1 3.88 E+0 1 2.93 E+0 1 1.59 E+0 3 9.28 E+0 1 6.48 E+0 0 1.64 E+0 2 6.41

MCB10 strategy

Quantit y

3.31

-p

OF-HH / kg NOx-eq

1.21E +03

% change to the CF strategyα 9.33

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IR/ kBq Co-60-eq

Qua ntity

1.24E+ 01

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SOD/ kg CFC11-eq

Quan tity

MCB5 strategy

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GWP / kg CO2-eq

MC strategy

-13.2

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Impact category

CF strate gy

-78.6 -15.6

-67.9

-79.1 -18.2

Journal Pre-proof E+0 02 E+02 2 α % change to the CF strategy: relative changes of the strategies of MC, MCB5, and MCB10 as compared to the CF strategy, respectively.

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Journal Pre-proof Table 4. Life cycle results of damage category (endpoint) under the four wheat production strategies. Damage category

Human health/ DALY Ecosystems/ species.yr-1

CF strate gy

MC strategy

Quant ity

Qua ntity

% change to the CF strategyα

Qua ntity

% change to the CF strategy

Qua ntity

% change to the CF strategy

4.33E -03

3.84 E-03

-11.5

3.75 E-03

-13.6

4.45 E-03

2.75

MCB5 strategy

1.61 1.43 1.47 -6.27 -16.9 -14.4 E-05 E-05 E-05 5.40 5.66 6.02 Resources/ 5.87E E+0 -8.04 E+0 -3.53 E+0 2.53 USD2013 +01 1 1 1 α % change to the CF strategy: relative changes of the strategies of MC, MCB5, and MCB10 as compared to the CF strategy, respectively.

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1.72E -05

MCB10 strategy

Journal Pre-proof CRediT author statement Zhixiang Jiang: Conceptualization, Methodology, Data curation, Software and formal analysis, Writing - review & editing, Funding acquisition. Hao Zheng: Conceptualization, Writing - review & editing, Funding acquisition.

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Baoshan Xing: Conceptualization, Supervision, Writing - review & editing.

Journal Pre-proof Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Baoshan Xing, Ph.D. Professor/Environmental & Soil Chemistry University of Massachusetts, Amherst e-mail: [email protected]

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☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:

Journal Pre-proof Highlights: 

Environmental LCA of wheat production with different strategies was compared



All the compost strategies showed lower environmental impacts



Biochar-amended manure compost strategies had a greater GWP mitigation

potential 

Compost and biochar production stages were the hotspots of environmental

impact Biochar addition rate of 5% (MCB5) was optimal due to its low environmental

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Figure 2

Figure 3

Figure 4

Figure 5

Figure 6